1. Field of the Invention
The present invention relates to an information processing apparatus such as a personal computer, and a program for decoding for use in the apparatus.
2. Description of the Related Art
In recent years, personal computers having AV functions similar to those of audio/video (AV) devices, such as a DVD (Digital Versatile Disc) player and a TV apparatus, have been developed.
This type of personal computer employs a software decoder that decodes compression-encoded motion video streams by software. The use of the software decoder enables a processor (CPU) to decode compression-encoded motion video streams, without the need to provide dedicated hardware.
Principal compression-encoding techniques include motion-compensation inter-frame prediction coding such as MPEG (Moving Picture Coding Experts Group) 2, or MPEG 4.
Jpn. Pat. Appln. KOKAI Publication No. 2001-245294 discloses a system in which a compression-encoded stream is decoded and an output video signal that is obtained by the decoding is subjected to post-filtering in order to improve the image quality. In order to prevent occurrence of frame dropping, this system makes use of a technique wherein the content of a filtering process that is to be executed in the post-filtering process is changed to reduce the time that is needed for the post-filtering process.
The post-filtering process, however, is a process that is executed outside the decoder. In a case where a delay occurs in the decoding process itself of the software decoder, even if the time needed for the post-filtering process is reduced, occurrence of frame dropping cannot be prevented.
Jpn. Pat. Appln. KOKAI Publication No. 2003-169337 discloses a system wherein a prediction picture is generated using a picture with fractional-pixel precision. In this system, in the case where a B-picture is decoded in order to reduce the amount of processing that is needed for a pixel interpolation process, the pixel interpolation for a reference picture is executed using a filter having a less number of taps than a filter that is used when a P-picture is decoded.
In the system of KOKAI No. 2003-169337, however, the filter with a small number of taps is always used when the B-picture is decoded. This leads to a decrease in image quality of reproduced video.
Jpn. Pat. Appln. KOKAI Publication No. 11-146398 discloses a system wherein an inverse DCT process for a P-picture or a B-picture is skipped in order to reduce the amount of processing that is needed for the inverse DCT process.
In the system of KOKAI No. 11-146398, however, the inverse DCT process for the P-picture or B-picture is always skipped, regardless of the value of the DCT coefficient. As a result, the image quality of reproduced video may considerably be degraded.
Recently, attention has been paid to H.264/AVC (Advanced Video Coding) standard as a next-generation motion picture compression-encoding technique. The H.264/AVC standard is a compression-encoding technique with a higher efficiency than the conventional compression-encoding technique such as MPEG2 or MPEG4. Thus, each of the encoding process and decoding process according to the H.264/AVC standard requires a greater amount of processing than in the conventional compression-encoding technique such as MPEG2 or MPEG4.
In a personal computer that is designed to decode a motion picture stream, which is compression-encoded by H.264/AVC standard, by software, if the load on the system increases, a delay would occur in the decoding process itself. Consequently, there is a danger that smooth motion picture reproduction cannot be executed.
Under the circumstances, it is necessary to provide a new function for realizing smooth motion picture reproduction.